Connecting Latitude D630 to external monitor

i had my Latitude D630 connected to a external monitor through a docking station for the past couple year's and now suddnely it stop working i looked in the website for similar post but non helped me , i try Fn key with f1 all the way to f12 and nothing helped i try extend screen it works but it only extend it to the external and what i need is the mirror image where i can close my lap top and work on the external . so am wondering what is the setting i need to applay because am 100% it's not a hardware issue beacuse it work's for couple minutes and then it goes back to the laptop screen and black out the external .